Positron emission tomography (PET) is a non-invasive imaging technique that detects positron annihilation events (e.g., coincidence or coincident photon events) along a line of response (LOR) using opposing PET detectors. Time of flight (TOF) PET measures a time difference of coincidence events at the PET detectors to determine a corresponding annihilation location along the LOR. Determination of an annihilation location within a predetermined margin of error is dependent on proper calibration of the detector's time resolution. PET systems, including TOF PET systems, commonly undergo a daily quality assurance (QA) procedure to verify a time calibration of the PET detectors. For diagnostic imaging, a loss of calibration between QA checks may generate inaccurate patient data and require the patient to repeat an imaging session.
In some applications, emission-guided radiation therapy (EGRT) uses an array of PET detectors to provide real-time location data of positron emissions originating from a patient tumor and a radiation source to therapeutically irradiate the tumor based on the location data. A loss of calibration of the PET detectors during an EGRT treatment session (e.g., between QA checks) and/or any degradation in the spatial resolution, temporal resolution, energy sensitivity and/or precision, as well as the inability to precisely determine the location of a patient tumor region relative to the therapeutic radiation source may lead to suboptimal radiation therapy treatment and damage to healthy tissue. Therefore, it may be desirable to provide real-time fault detection in a TOF PET system that may more quickly identify a time calibration error and/or faulty PET detectors.